Conventionally, various types of product testings are carried out with respect to tires in a finished state to measure uniformity (homogeneity), dynamic balance and outer shape thereof, and a tire testing device for carrying out such product testing is provided with a pair of rims which clamp a tire to be tested and support it. There are various types of rims in accordance with the size of the tire which is supported by the rims, so that in case the size or type of the tire to be tested changes, the rims need to be changed as well. Thus, a rim replacing device for replacing such rims is installed in the conventional tire testing device.
As such rim replacing devices, a device, which has a spindle, for instance, and a claw section for fixing a rim to this spindle, is known. This claw section has a base end side section and a hook-like tip end side section which is swingably provided with respect to the base end side section. The rim replacing device further has driving means, such as an actuator, for driving the claw section to swing and fixing the rims to the spindle side.
However, in such a rim replacing device for fixing a rim using a claw section in this way, its construction is likely to become complex, leading to an increase in device costs and making its maintenance difficult.
Accordingly, Patent Document 1 as described hereinafter discloses a rim replacing device having permanent magnets provided therein. In this device, rims are fixed to a spindle due to a magnetic force generated by the permanent magnets and the rims are replaced by detaching them from the spindle against the magnetic force generated by the permanent magnets.
However, a variety of problems caused by the permanent magnets may occur in this device.
For instance, a strong magnetic force is required for the permanent magnets in order to fix the rims to the spindle, but most permanent magnets capable of generating such a strong magnetic force are made of brittle materials such as ferrite, and when a slightly stronger impact is applied to such a brittle material, it is likely to break. Breakage of the permanent magnets will lead to fragment scatter, making handling thereof following such breakage cumbersome.
In this device, as the permanent magnets are brought closer to a mounting section, a force (magnetic attraction force) with which these elements attract each other due to the magnetic force generated by the permanent magnets becomes stronger, and the permanent magnets may strongly hit the mounting section due to such force, which is likely to cause it to break. Alternatively, breakage of a permanent magnet can also occur, when the permanent magnet is installed in a mounting hole, and if the permanent magnet is accidentally strongly attracted to an inner circumferential surface of a mounting recess or a spindle surface at a periphery of an opening of the mounting recess. When magnet fragments produced when the permanent magnet breaks as described above are scattered, they easily magnetically attach, for instance, to the inner circumferential surface of the mounting recess or the surface of the spindle, and a fragment removal operation becomes necessary, causing a decrease in productivity.
In the rim replacing device according to Patent Document 1, to mount an upper rim to an upper spindle, permanent magnets for attracting the upper rim to the upper spindle due to magnetic force are mounted in the upper spindle, and to remove the upper rim from the upper spindle, a transmission rod is provided in the upper spindle to depress the upper rim downward and detach it from the upper spindle, which may cause the following problems to occur in the tire testing device.
In the rim replacing device, as a detaching device for detaching the upper rim from the upper spindle needs to be provided at a position where permanent magnets are not present, installation of the detaching device reduces a space capable of housing the permanent magnets, so that the number of permanent magnets which can be provided is reduced. On the one hand, in response to the recent increase in diameter of rims, there is much request for devices which can handle a larger number of permanent magnets and enable fixing of heavyweight rims. The device disclosed in the Patent Document 1 cannot sufficiently satisfy these demands.
In the rim replacing device according to Patent Document 1, the transmission rod is provided so as to move inside a guide sleeve provided in a flange, for instance, of the upper spindle, so that at the time of tire testing, the transmission rod and the guide sleeve are rotated together with the upper spindle, and a resulting error component is applied to uniformity measurement data, which can cause a decrease in the uniformity measuring accuracy.
[Related Art Document]
[Patent Document]
[Patent Document 1] Japanese Patent No. 2626902 (refer to FIG. 1, FIG. 2 and FIG. 3)